A wide range of electronic circuits employ printed circuit cards. These printed circuit cards in general have come to be manufactured by automatic fabrication machines in recent years. A variety of automatic IC component mounting apparatuses or automatic assemblers have been proposed and put to practical use.
The electronic components mounted on the printed circuit cards have many parallel leads arranged on all sides. If an integrated circuit component has any bent leads, current connection between the IC component and the wiring pattern on the card cannot be obtained. To avoid this, inspection must be made to detect any deformed leads so that only those IC components with correct leads can be brought onto the printed circuit card.
Explanation will be given as to the bent leads by referring to FIG. 2. FIG. 2(a) is a plan view of a flat package type IC component, in which reference numeral 1 represents a body of the integrated circuit component and 2 represents its leads. Bent leads are shown by 2a and 2b. FIG. 2(b) is a side view showing bent leads 2c and 2d. In the following description, the bend of the leads 2a, 2b in FIG. 2(a) along the direction of the row of leads is called a lateral bend while that of the leads 2c, 2d in FIG. 2(b) in a direction perpendicular to the row is called a vertical bend.
The automatic assembler has a suction hand to carry IC components placed at a specified location to the printed circuit card and to correctly position the IC components on the card. This process is done as follows. After holding an IC component, the suction hand is stopped at a predetermined position and the IC component holding position of the suction hand is checked. According to the result of the check of the holding position, the suction hand position on the card is controlled to ensure a sufficient accuracy for the IC component mounting position. For detection of the IC component holding position of the suction hand, a video camera is used to take a picture of the IC component held on the suction hand to obtain plan view image data, from which the IC component holding position is determined. This is a conventional method of positioning.
Taking advantage of the image data, various method of checking for bent leads are possible.
Although these methods are not published in technical literatures, one example technique is to digitize the image data into binary values, calculate by using the digitized data the center of gravity of each lead, detect the distance between the gravity centers as a lead pitch, and compare the calculated lead pitch with a preset value to detect any bent lead.
To apply this method to the bent lead detection, however, requires a reasonably high resolution of the image data, so that the image data that is used for detecting the IC component holding position is not sufficient. Bent lead detection also requires additional data, such as a wide-angle view of image data with larger number of pixels, which causes various problems, such as a necessity to take pictures several times for each IC component and an increased data processing time, prolonging the card assembly processing time. That is, since the above conventional technique uses digitized binary image data, those data concerning the edges of leads easily become unstable, making it difficult to measure the lead pitch of general size or about 0.3 mm with high accuracy. Therefore, image data as obtained through the wide-angle view which has a greater number of pixels is needed. That is, the common use of the image data that is intended for the position detection in the automatic assembler fails to meet the requirements for the bent lead detection. And application of such a technique to the bent lead detection will result in an increase in the processing time for each IC component.
The inventor has proposed an invention associated with the Japanese Patent Application No. 147066/1986, which disclosed a technique whereby the plan view image data of an IC component is used to extract data concerning the part of leads where they are transversely cut by a straight line running parallel with the row of leads and, according to the pattern of shading of the extracted data, any lead bend is detected.
A series of leads of the flat package type IC component, when photographed using reflected light, produces a lighter image than the background, providing a certain contrast. Depending on the angle of reflection from the lead, the reflected light quantity changes, exhibiting less contrast with the background. Thus, for the leads with such characteristics, the brightness distribution on a measuring line (straight line) running across the series of leads and along the lead row exhibits a periodical variation according to the condition of lead arrangement.
The above-mentioned patent application makes use of this shade variation to allow easy detection of any bent leads in the components.
A Japanese Patent Application Laid-Open No. 1900/1985 may be cited as an example of the above technique.
These preceding patent applications, however, have a drawback that since the relative positional relationship with adjacent leads is used for detecting the lateral bend of a lead, when a plurality of leads are bent in the same direction as a whole, detection of bends is difficult. The foregoing patent applications have no considerations in this regard and therefore an error would occur in the measurement of the coordinates of the IC component's center position and of angular misalignment.